U.S. Pat. Nos. 6,084,702; 6,446,402; 7,525,717; 7,538,931; 7,542,196; 7,817,328 and 8,018,639 describe thermochromic films and devices for use in Sunlight Responsive Thermochromic™ windows and other applications of thermochromic systems. These patents are hereby incorporated by reference. Of particular interest for use in thermochromic films are thermochromic materials based on ligand exchange of transition metal ions wherein one of the ligands exchanged is the iodide anion. As disclosed in U.S. Pat. Nos. 7,525,717; 7,538,931; 7,542,196; and 8,018,639, Co(II) and Ni(II) form strong visible light absorbing systems when Co(II) and Ni(II) form complexes involving iodide as at least one type of ligand on these metal ions. When certain of these systems are heated, large changes in absorbance take place in the visible and/or near infrared spectral ranges. The concentration of strong visible light absorbing, iodide containing complexes increases with increasing temperature and decreases with decreasing temperatures in a continuous and reversible manner in these thermochromic systems and films.
However, thermochromic systems and films comprising iodide are prone to residual yellow color formation during preparation, storage and/or use of the systems or film. This yellow color formation may be due to air sensitivity causing iodide to be oxidized by oxygen to iodine or tri-iodide. Whatever the cause, these thermochromic systems and films tend to become undesirably yellow or have an unacceptable increase in the room temperature color coordinate b* value of the system on prolonged air exposure, (for the definition of the CIELAB color coordinate b* see Color Science: Concepts and Methods, Quantitative Data and Formulae, 2nd Ed. J. Wiley & Sons: New York, 1982). Once a thermochromic film is laminated between sheets of glass much of the oxygen exposure is eliminated. While edge seals may be effective at eliminating ingress of oxygen into the film from the edges, providing seals is not always practical. Thus there is a need to minimize or eliminate the air sensitivity of thermochromic systems and films during manufacture and storage prior to lamination; and minimize or eliminate the air sensitivity of the edges of laminates once the laminates are used, such as in windows.